A polymer electrolyte fuel cell is a fuel cell in which a polymer solid electrolyte is sandwiched between an anode and a cathode, a fuel is supplied to the anode, and oxygen or air is supplied to the cathode, whereby oxygen is reduced at the cathode to produce electricity. As the fuel, hydrogen, methanol, or the like is mainly used.
To enhance a reaction rate in a fuel cell and to enhance the energy conversion efficiency of the fuel cell, a layer containing a catalyst (hereinafter also referred to as a “fuel cell catalyst layer”) has been conventionally disposed on the surface of a cathode (air electrode) or the surface of an anode (fuel electrode) of the fuel cell.
As such a catalyst, noble metals have been generally used, and among the noble metals, platinum, which is stable at a high potential and has a high activity, has been mainly used. However, since these noble metals are expensive and limited in resource amount, development of alternative catalysts has been desired.
Under these circumstances, the research of iron-containing catalysts as a catalyst alternative to noble metals is underway.
Iron is more inexpensive and its resource amount is abundant, compared with noble metal materials such as platinum.
Patent Literature 1 discloses a process for producing an iron-containing activated carbon obtained by heat-treating an activated carbon and an iron protein, and describes a fuel cell catalyst containing this activated carbon.
Patent Literature 2 discloses a process for producing an iron-containing carbon raw material including steps of mixing an iron salt, a nitrogen-containing compound and a carbohydrate and heat-treating the mixture in an inert atmosphere, and describes a fuel cell catalyst containing this raw material.
Non-Patent Literature 1 discloses a catalyst composed of an iron-containing carbide obtained by heat-treating erythrocyte containing, as a main component, hemoglobin, which is an iron protein.
Non-Patent Literature 2 discloses a catalyst where an iron atom is bonded to a carbon material, which is prepared by supporting a macrocyclic complex of iron on a carbon material, and then heat-treating the supported iron complex in an inert atmosphere.
Non-Patent Literature 3 discloses a fuel cell catalyst composed of a metal alloy carbon obtained by incorporating iron in the form of an acetylacetonato complex or a phthalocyanine complex to a carbon raw material organic matter and carbonizing the mixture.
Conventional catalysts alternative to noble metals including iron-containing catalysts as described above provide a certain level of performance, but their oxygen reducing ability is insufficient, and their performance is unsatisfactory in practical uses.